Growing groups III-V lateral nanowire channels

ABSTRACT

In one example, a method for fabricating a semiconductor device includes forming a mandrel comprising silicon. Sidewalls of the silicon are orientated normal to the &lt;111&gt; direction of the silicon. A nanowire is grown directly on at least one of the sidewalls of the silicon and is formed from a material selected from Groups III-V. Only one end of the nanowire directly contacts the silicon.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to semiconductor devices and relates more specifically to field effect transistors fabricated in accordance with complementary metal-oxide-semiconductor technology and including laterally grown nanowire channels.

BACKGROUND OF THE DISCLOSURE

Groups III-V semiconductor materials have been shown to be superior to silicon for particular applications, including, for example, optoelectronic applications. In such applications, a layer of a Group III-V material may be grown over a semiconductor substrate in a pillar shape, with a narrow diameter and a height which is sufficiently long compared the diameter. When the diameter of the Group III-V material is narrowed to a few tens of nanometers, the resultant structure may be referred to as a “nanowire.”

SUMMARY OF THE DISCLOSURE

In one example, a method for fabricating a semiconductor device includes forming a mandrel comprising silicon. Sidewalls of the silicon are orientated normal to the <111> direction of the silicon. A nanowire is grown directly on at least one of the sidewalls of the silicon and is formed from a material selected from Groups III-V. Only one end of the nanowire directly contacts the silicon.

In another example, a method for fabricating a semiconductor device includes forming a mandrel. The mandrel comprises a layer of silicon and a mask layer formed directly on the layer of silicon. A growth mask is deposited directly on the mandrel, and a photoresist layer is deposited directly on the growth mask. The photoresist layer is patterned, resulting in the removal of a portion of the photoresist layer. Portions of the growth mask that resided directly beneath the removed portion of the photoresist layer are then etched to expose a portion of the sidewalls. A nanowire is grown directly on the portion of the sidewalls. The nanowire is formed from a material selected from Groups III-V, and only one end of the nanowire directly contacts the layer of silicon.

In another example, a semiconductor device includes a mandrel comprising silicon. The sidewalls of the silicon are orientated normal to a <111> direction of the silicon. A nanowire is grown directly on at least one of the sidewalls. The nanowire is formed from a material selected from Groups III-V, and only one end of the nanowire directly contacts the silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present disclosure can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIGS. 1A-1H illustrate a semiconductor device during various stages of a first fabrication process performed according to examples of the present disclosure;

FIGS. 2A-2D illustrate a semiconductor device during various stages of a second fabrication process performed according to examples of the present disclosure; and

FIG. 3 illustrates an isometric view of a semiconductor device including multiple laterally grown nanowire channels.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the Figures.

DETAILED DESCRIPTION

In one example, a method for growing Groups III-V lateral nanowire channels is disclosed. Semiconductor materials such as Groups III-V materials have been used to form nanowire channels in field effect transistors (FETs). These channels are grown in a manner that results in the channels being orientated vertically relative to the substrate surface. From a complementary metal-oxide-semiconductor (CMOS) integration point of view, this approach presents several challenges. For example, epitaxial growth of Groups III-V semiconductors on silicon may be complicated by lattice mismatch, differences in crystal structure, and/or differences in thermal expansion coefficients, among other complications.

Examples of the present disclosure grow Group III-V lateral nanowire channels in a manner that is compatible with CMOS integration. In one example, the nanowires are grown laterally on a sidewall of a silicon mandrel. By limiting the growth area to the sidewall, nanowire channels can be formed in a manner that is easier to incorporate into existing CMOS integration schemes than vertically orientated channels.

FIGS. 1A-1H illustrate a semiconductor device 100 during various stages of a first fabrication process performed according to examples of the present disclosure. As such, when viewed in sequence, 1A-1H also serve as a flow diagram for the first fabrication process. In particular, FIGS. 1A-1H illustrate isometric views of the semiconductor device 100 during the various stages of the first fabrication process.

Referring to FIG. 1A, one example of the semiconductor device 100 begins as a substrate 102, formed, for example, from bulk silicon (Si). A buried oxide (BOX) layer 104 is formed directly on the substrate 102. A silicon layer 106 is formed directly on the buried oxide layer 104. The silicon layer 106 may be formed, for example, from a bulk silicon wafer or a silicon-on-insulator (SOI) wafer. In one example, the silicon layer 106, whether formed from bulk silicon or SOI, is a (110) silicon wafer (i.e., the wafer is flat in the <110> direction, as illustrated by the coordinate axes). An etch mask 108 is formed directly on the silicon layer 106. The etch mask 108 may be formed, for example, from silicon dioxide (Sift), silicon nitride (SiN_(x)), or aluminum oxide (Al₂O₃). FIG. 1A illustrates the semiconductor device 100 after patterning of the etch mask 108, which may be performed using a dry etch process and results in the removal of a portion of the etch mask 108 down to the silicon layer 106. The patterning defines dimensions of at least one mandrel 110 formed partially of the etch mask material (only one mandrel 110 is illustrated in FIG. 1A for clarity). The mandrel 110 is orientated such that its longest dimension is parallel to the <112> direction of the silicon layer 106, as illustrated by the coordinate axes.

As illustrated in FIG. 1B, the silicon layer 106 is next etched, for example using an anisotropic wet etch process (using, for instance, potassium hydroxide or tetramethylammonium hydroxide). In one example, etching of the silicon layer 106 results in the removal of any portions of the silicon layer 106 that do not reside directly beneath the etch mask 108. As a result, the mandrel 110 whose dimensions were defined in FIG. 1A includes both a portion of the etch mask 108 and a portion of the silicon layer 106. The silicon portion of the mandrel 110 has a vertical sidewall that is orientated in a manner that is normal to the <111> direction of the silicon layer 106, as illustrated by the coordinate axes. The vertical sidewall has an atomically flat surface due to the facet-selective nature of the etching process.

As illustrated in FIG. 1C, a growth mask 112 is next deposited over the semiconductor device 100, directly on the buried oxide layer 104 and the mandrel 110. The growth mask may be formed, for example, from an oxide.

As illustrated in FIG. 1D, a photoresist layer 114 is next deposited directly on the growth mask 112. FIG. 1D illustrates the semiconductor device 100 after patterning of the photoresist layer 114, which results in the removal of a portion of the photoresist layer 114 down to the growth mask 112.

As illustrated in FIG. 1E, the portions of the growth mask 112 that do not reside directly beneath the photoresist layer 114 are next etched down to the buried oxide layer 104, for example using a wet etch process. Etching of the growth mask results in the exposure of a portion of the sidewalls of the silicon layer 106 and the etch mask 108, as illustrated.

As illustrated in FIG. 1F, the photoresist layer 114 is next removed entirely. In addition, a portion of the growth mask 112 (i.e., the portion of the growth mask 112 that does not directly contact the silicon layer 106 or the etch mask 108) is optionally also removed.

As illustrated in FIG. 1G, an epitaxial nanowire 116 is next grown laterally, i.e., on the sidewall of the silicon layer 106. In one example, the nanowire 116 comprises a material selected from Groups III-V. In one example, the nanowire 116 is grown only on the sidewall of the silicon layer 106, and the longest dimension of the nanowire 116 is parallel to the <111> direction of the silicon layer 106, as illustrated by the coordinate axes. Thus, growth is significantly greater in the <111> direction than it is in the <110> and <112> directions (or in the directions normal to the <111> direction). The nanowire 116 may be grown on both sidewalls of the silicon layer 106, as illustrated; however, only one end of each segment of the nanowire 116 contacts the silicon layer 106. Although only one nanowire 116 is illustrated in FIG. 1G, any number of nanowires 116 may be similarly formed, with high density and small pitch.

As illustrated in FIG. 1H, a metal gate 118 is next formed on the nanowire 116. Thus, the portion of the nanowire 116 residing directly beneath the metal gate 118 functions as a conducting channel. The metal gate 118 may be formed from a high-k metal. The portions of the nanowire 116 residing on either side of the gate are modified, e.g., via ion-implantation or epitaxy, to function as source and drain regions.

The resultant nanowires may thus form the conducting channels of a transistor. Thus, Groups III-V semiconductor nanowire channels may be grown directly on a silicon surface orientated normal to the surface of the device substrate. As discussed above, this results in nanowires whose longest dimension is parallel to the <111> direction of the silicon surface, i.e., nanowire growth is significantly greater in the <111> direction than it is in the <110> direction. This allows multiple nanowires to be grown with high density and low pitch, maximizing use of device space.

The process illustrated in FIGS. 1A-1H may be modified. FIGS. 2A-2D, for instance, illustrate a semiconductor device 200 during various stages of a second fabrication process performed according to examples of the present disclosure. As such, when viewed in sequence, 2A-2D also serve as a flow diagram for the second fabrication process. In particular, FIGS. 2A-2D illustrate isometric views of the semiconductor device 200 during the various stages of the second fabrication process.

As illustrated in FIG. 2A, rather than start with a silicon substrate and bulk oxide layer, the semiconductor device 200 simply starts with a bulk silicon wafer 202. In one example, the wafer 202 is a (110) silicon wafer (i.e., the wafer 202 is flat in the <110> direction, as illustrated by the coordinate axes). An etch mask 204 is deposited directly on the wafer 202 and is patterned, similar to the process illustrated in FIG. 1A. The etch mask 204 may be formed, for example, from silicon nitride (SiN_(x)). The wafer 202 is next partially etched, for example using an anisotropic wet etch process (using, for instance, potassium hydroxide or tetramethylammonium hydroxide). In one example, etching of the wafer 202 results in the removal of some (but not all) portions of the wafer 202 that do not reside directly beneath the etch mask 204. As a result, a mandrel 208 formed in FIG. 2A that includes both a portion of the etch mask 204 and a portion of the wafer 202. The silicon portion of the mandrel 110 has a vertical sidewall that is orientated in a manner that is normal to the <111> direction of the wafer 202, as illustrated by the coordinate axes. The vertical sidewall has an atomically flat surface due to the facet-selective nature of the etching process. Thus, the result of this process is similar to the result illustrated in FIG. 1B (without the substrate 102 and buried oxide layer 104).

As illustrated in FIG. 2B, an oxide layer 206 is next deposited directly on the wafer 202 and etch mask 204. The oxide layer may comprise, for example, silicon dioxide (SiO₂).

As illustrated in FIG. 2C, the oxide layer 206 is next polished down to the etch mask 204.

As illustrated in FIG. 2D, the oxide layer 206 is next partially etched to expose the silicon sidewalls of the mandrel 208. Further fabrication of the semiconductor device 200 may now proceed in a manner similar to that described above in connection with FIGS. 1C-1H. Thus, the process illustrated in FIGS. 2A-2D is an alternative to the process illustrated in FIGS. 1A-1B.

The process illustrated in FIGS. 1A-1H (optionally substituting the process illustrated in FIGS. 2A-2D for that illustrated in FIGS. 1A-1B) may be used to fabricate any number of semiconductor nanowire channels. FIG. 3, for example, illustrates an isometric view of a semiconductor device 300 including multiple laterally grown nanowire channels 302 ₁-302 _(n) (hereinafter collectively referred to as “nanowire channels 302”). In this example, the nanowire channels 302 are physically separated along the <112> direction of the silicon 306 by oxide regions 304 ₁-304 _(n+1) (hereinafter collectively referred to as “oxide regions 304”). The oxide regions 304 may comprise, for example, the growth mask 112 discussed in connection with FIGS. 1A-1H.

Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. 

What is claimed is:
 1. A method for fabricating a semiconductor device, the method comprising: forming a mandrel comprising silicon, wherein sidewalls of the silicon are orientated normal to a <111> direction of the silicon; and growing a nanowire directly on at least one of the sidewalls, wherein the nanowire is formed from a material selected from Groups III-V, and wherein only one end of the nanowire directly contacts the silicon, wherein the growing comprises: depositing a growth mask directly on the mandrel; depositing a photoresist layer directly on the growth mask; patterning the photoresist layer, wherein the patterning results in a removal of a portion of the photoresist layer; etching portions of the growth mask that resided directly beneath the portion of the photoresist layer, such that a portion of the sidewalls is exposed; and growing the nanowire epitaxially on the sidewall, wherein a majority of the growing occurs in the <111> direction.
 2. The method of claim 1, further comprising: forming a metal gate over a portion of the nanowire; and modifying portions of the nanowire over which the metal gate is not formed to create source and drain regions.
 3. The method of claim 2, wherein the modifying is performed using ion-implantation.
 4. The method of claim 2, wherein the modifying is performed using epitaxy.
 5. A method for fabricating a semiconductor device, the method comprising: forming a mandrel, wherein the mandrel comprises a layer of silicon and a mask layer formed directly on the layer of silicon, and wherein sidewalls of the layer of silicon are orientated normal to a <111> direction of the layer of silicon; depositing a growth mask directly on the mandrel; depositing a photoresist layer directly on the growth mask; patterning the photoresist layer, wherein the patterning results in a removal of a portion of the photoresist layer; etching portions of the growth mask that resided directly beneath the portion of the photoresist layer, such that a portion of the sidewalls is exposed; growing a nanowire directly on the portion of the sidewalls, wherein the nanowire is formed from a material selected from Groups III-V, and wherein only one end of the nanowire directly contacts the layer of silicon.
 6. The method of claim 5, wherein a longest dimension of the nanowire is parallel to a <111> direction of the silicon.
 7. The method of claim 5, wherein the silicon comprises (110) silicon.
 8. The method of claim 5, wherein a longest dimension of the mandrel is orientated parallel to a <112> direction of the silicon.
 9. The method of claim 5, further comprising: forming a metal gate over a portion of the nanowire; and modifying portions of the nanowire over which the metal gate is not formed to create source and drain regions.
 10. The method of claim 9, wherein the modifying is performed using ion-implantation.
 11. The method of claim 9, wherein the modifying is performed using epitaxy.
 12. The method of claim 5, wherein the semiconductor device is a transistor.
 13. The method of claim 5, wherein the semiconductor device is part of an optoelectronic device.
 14. The method of claim 1, wherein a longest dimension of the nanowire is parallel to the <111> direction of the silicon.
 15. The method of claim 1, wherein the silicon comprises (110) silicon.
 16. The method of claim 1, wherein a longest dimension of the mandrel is orientated parallel to a <112> direction of the silicon.
 17. The method of claim 1, wherein the forming comprises: forming a buried oxide layer directly on a substrate; providing the silicon as a layer directly on the buried oxide layer; forming an etch mask directly on the silicon; patterning the etch mask to define dimensions of the mandrel; and etching the silicon down to the buried oxide layer to remove portions of the silicon not residing directly beneath the dimensions of the mandrel.
 18. The method of claim 1, wherein the forming comprises: providing the silicon as a bulk wafer; forming an etch mask directly on the silicon; patterning the etch mask to define dimensions of the mandrel; and etching the silicon to remove some, but not all, of the silicon not residing directly beneath the dimensions of the mandrel. 